Shoulder pain following stroke is a major rehabilitation problem affecting approximately 60% of moderate to severely impaired stroke survivors. The investigative team demonstrated the efficacy of short-term, percutaneous intramuscular (IM) peripheral nerve stimulation (PNS) in treating shoulder pain following stroke. However, only those individuals who received treatment within 18 months of their stroke experienced enduring treatment effect. Those treated after 18 months experienced significant pain reduction at the end of treatment, but pain returned within 3 months. To treat this more challenging population, an exploratory placebo controlled, randomized controlled trial is proposed to demonstrate the safety and efficacy of a fully implantable PNS System. The trial has 2 stages. During the Trial Stage, participants who experience benefit from short-term percutaneous IM PNS, but in whom pain returns are identified. During the Implant Stage, these participants receive the fully implanted IM PNS system and are randomized to receive IM PNS or a second course of short-term percutaneous IM PNS treatment. Outcomes include pain, motor impairment, ADLs and quality of life. In order to explore mechanisms, participants in both Stages undergo quantitative sensory and motor testing.